1. Field of the Invention
This invention relates to microprocessor systems. In particular, the invention relates to the conversion between serial bus cycles and parallel port commands.
2. Description of Related Art
Many serial buses are now available for interfacing peripheral devices to a computer system. Examples of these buses include the Universal Serial Bus (USB) and the Institute of Electrical and Electronics Engineers (IEEE) 1394 standard bus. These serial buses provide a simple method of attaching and accessing peripheral devices.
For example, the USB is a new standard that complements the traditional interfaces via the microprocessor bus such as the Peripheral Component Interconnect (PCI), Industry Standard Architecture (ISA), or Enhanced Industry Standard Architecture (EISA) buses. Advantages of the USB include plug and play support, hot attachment, expandability, legacy hardware and software support, and low cost.
A USB-based system typically includes one or more USB clients, a USB host controller, one or more hubs, and several USB devices. Examples of USB devices are USB-compatible digital cameras, printers, keyboards, scanners, modems, and digital phones. All USB devices attach directly to a USB controller or via a USB hub that provides one or more ports. USB supports two different speeds: 1.5 Mega bits (Mbits) per second for low-speed devices and 12 Mbits/second for high-speed devices.
The transfer types supported by the USB include isochronous transfers, bulk transfers, interrupt transfers, and control transfers. USB communication is based on transferring data at regular intervals of 1 millisecond (ms). Each interval is referred to as a frame. Each USB function is designed with a collection of registers, or endpoints, used by the client driver when accessing its function. An endpoint, or a device endpoint, is a uniquely identifiable portion of a USB device that is the source or sink of information in a communication flow between the host and device.
An interrupt transfer is used for devices that are typically interrupt driven devices in legacy personal computer (PC) implementations. A bulk transfer is used for transferring large blocks of data that have no periodic or transfer rate requirement (e.g., large print job).
An isochronous transfer requires a constant delivery rate. Applications that use isochronous transfers should ensure that rate matching between the sender and receiver can be accomplished. A control transfer is used to transfer specific requests to USB devices and is most commonly used during device configuration.
Although these serial buses have become standards endorsed by the industry such as the computer industry, not all systems or platforms provide the serial bus interface directly. A PC system without a serial bus interface therefore has problems communicating with a serial bus device.
Therefore there is a need in the technology to provide an efficient method and apparatus to provide communication between a serial bus device and a parallel port, especially the conversion between serial bus cycles and parallel port commands.